Aircraft: LARGE TRANSPORT; LOW WING; 2 TURBOJET ENG
Phase of flight: taxi
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence

There were thunderstorms forecast and planned for. We had a routing to avoid as much of the weather as possible and an alternate of Tampa with a FAR :45 of 4;000 LBS and a planned land at MCO via the PIGLT 4 arrival of 10;100 LBS. I was the pilot flying. During our arrival; we were rerouted to the north over OTK to avoid a large cell. Then; having done that; ATC changed their mind and re-routed us over LEGGT and PIE for the COSTR arrival. The landing runways switched from 18 to 36. On the COSTR arrival we overflew our planned divert; where the weather looked good. As we approached the field; the airport switched back to landing south and we were assigned a visual approach to 18R. Upon switching to Tower frequency; we overheard the 757 landing in front of us; stating that windshear was not encountered on final. At about 2;000 FT MSL and past the final approach fix we got a microburst alert for our runway of a 40 KT loss. We verified that it was an alert and for our runway and executed a missed approach; we had no other indication of windshear. We were then vectored back around for another visual approach to 18R. The conditions visually still looked fine. Prior to the final approach fix; we were told that the runway was still in alert; but improving and we decided to hold for 1 turn at the final approach fix at 3;000 FT. On the downwind leg of that first hold; we were told that the alert was downgraded to a windshear alert at 25 then 20 KTS and improving. We were still very close to our divert fuel + FAR :45 (the Captain remembers just over 6;000 LBS); the field still visually looked fine; and there were no other signs of windshear. We decided to give it another try. Once again; inside the FAF; the Tower gave us a Microburst Alert and we immediately decided to execute a missed approach and divert to our planned alternate of TPA. While receiving vectors; we were informed that Tampa was closed. Given that and taking into account the existing cells near MCO; we decided and informed ATC that we wanted to divert to West Palm Beach. The initial vectors to West Palm were to the Northeast and at 4;000 FT to avoid the cell that was impacting the airport. We declared minimum fuel with ATC at that time; sent an ACARS to Dispatch informing him about the divert and asking about West Palm Beach; and also continued around the cell followed soon after by vectors direct to West Palm Beach. After a short period; we received a response from Dispatch asking us if SRQ was OK; but by then we were committed to the east coast of Florida by our position and the weather. As we started our climb to 20;000 FT; we loaded the FMGC with the PBI divert. The forecast land fuel was 2;400 LBS and the PBI weather was VFR. 2;400 LBS was clearly emergency fuel to the Captain and me; and at that moment we were overflying Melbourne; FL; which was in the clear and with which; I was familiar. I knew they had a 10;000 FT runway; commercial service; good weather; and that 2;400 LBS in PBI was too low. We did a quick check in the FMGC for nearest alternates and found no better alternative (Patrick AFB etc). We slowed to max L/D (Green Dot) and sent a query to Dispatch about Melbourne. After a couple of minutes with no response; the Captain; demonstrating excellent CRM/TEM skills; convinced me that landing at PBI with such little fuel was a bad plan either way; and so about 10 miles South of Melbourne at 20;000 FT we decided to divert to Melbourne. We quickly obtained the weather; coordinated with ATC; and programmed the visual approach into the FMGC. We landed with approximately 3;600 LBS and blocked in (according to the pre-service fuel on the outbound leg back to Orlando) with 3;300 LBS. That was clearly a better plan than West Palm Beach with 2;400 LBS or potentially less. After block in; I noticed that our last message telling Dispatch about our divert to Melbourne was still on the scratch pad; i.e. the send prompt was probably pressed inadequately in the heat of the battle and that message was never sent. In any case; we both felt strongly that we did not have the time to wait for coordination from Dispatch as there was no better alternative. In retrospect; we should have declared an emergency because our fuel state didn't allow us the time to coordinate. Our thinking was that we avoided the emergency fuel situation by diverting to Melbourne; but Melbourne was not an authorized divert field for this aircraft thus requiring the emergency declaration anyway. I believe that it was the right field to land at; as it was a safe good weather field (and a regular airport for [similar aircraft types to ours]); but we should have declared an emergency before landing there. Thunderstorms throughout Florida caused delays and vectors in our arrival to MCO. Our route brought us near TPA and PIE and we checked weather for those airports. We received vectors around cells between PIE and MCO. During our downwind on right traffic to RWY 18R we saw the runway and were cleared for a visual approach to RWY 18R to cross ORL 2;500 FT or above. Approximately 2;000 FT Tower reported a Microburst Alert; 40 KT winds and the First Officer executed a missed approach. We were vectored around weather to another downwind. Approach Control asked us why we diverted; and they were not aware of the alert. They reported it had dissipated and we were vectored to a 2nd approach to 18R. We accepted the ILS 18R and the runway was in sight. During the approach Tower reported another Microburst Alert; winds at 50 knots. And offered holding on the final approach course to wait until it dissipated. During our first turn in holding the Alert was gone and we started to the runway. Shortly after they had another Microburst Alert on our runway and we executed another missed approach. Fuel to TPA was 2;090 and 22 min. This would put us just under our FAR fuel of 4;021. Just as our weather check showed TSRW we were informed that TPA was closed. My First Officer was familiar with Florida airports and suggested PBI. We informed Dispatch we were going to PBI; informed ATC and were currently being vectored north and east around another cell to the east. I declared minimum fuel. When heading south towards PBI the FMGC showed us arriving with 2;400 LBS of fuel. I was about to declare Emergency fuel when the Controller gave us vectors away from direct PBI. The ATC Controller was unaware we had already declared minimum fuel with the previous Controller. We saw MLB in front of us. It was clear for miles. Further down the coast there was some more weather towards PBI. The First Officer said he was familiar with MLB. We asked the Dispatcher about MLB and he suggested SRQ. SRQ would have required vectors around huge thunderstorms. Our choice was emergency fuel to PBI and possibly more weather; landing with less than 2;400 LBS. or going into MLB with a visual approach; 10;000 FT runway; no terrain or obstacles; landing with close to FAR fuel; on a runway used by C17's and 747's; and the runway was selectable in the FMGC. We informed the Dispatcher we were going to MLB. The First Officer was flying and familiar with MLB. I was not familiar with PBI or MLB. I felt MLB was the better choice and the First Officer concurred. After an uneventful landing we taxied to the gate and arrived with 3;300 LBS. of fuel at shutdown. This was a very dynamic environment. Decisions had to be made very quickly. Options were changing and disappearing fast. I was distracted explaining to ATC that we had already declared minimum fuel and in hindsight I should have declared emergency fuel at that moment. The First Officer was extremely helpful and he did an excellent job. Air carrier flight crew reports being vectored for weather during arrival to MCO then executing two missed approaches due to microburst alerts from the Tower. The decision is made to divert to their filed alternate and is informed it is closed due to weather. The crew then decides to divert to the nearest suitable alternate and lands with 3;600 LBS of fuel.